Embedded nanoparticle films and method for their formation in selective areas on a surface

ABSTRACT

The invention is directed to a method of positioning nanoparticles on a patterned substrate. The method comprises providing a patterned substrate with selectively positioned recesses, and applying a solution or suspension of nanoparticles to the patterned substrate to form a wetted substrate. A wiper member is dragged across the surface of the wetted substrate to remove a portion of the applied nanoparticles from the wetted substrate, and leaving a substantial number of the remaining portion of the applied nanoparticles disposed in the selectively positioned recesses of the substrate. The invention is also directed to a method of making carbon nanotubes from the positioned nanoparticles.

This application is a Division of co-pending U.S. patent applicationSer. No. 13/611,636 filed Sep. 12, 2012 (allowed), which is a Divisionof U.S. patent application Ser. No. 13/399,612 filed Feb. 17, 2012, nowU.S. Pat. No. 8,323,608 issued Dec. 4, 2012, which is a Division of U.S.patent application Ser. No. 12/701,977 filed on Feb. 8, 2010, now U.S.Pat. No. 8,187,565 issued May 29, 2012, which is a Continuation of U.S.patent application Ser. No. 12/197,688 filed on Aug. 25, 2008, now U.S.Pat. No. 7,682,591 issued Mar. 23, 2010, which is a Continuation of U.S.patent application Ser. No. 11/400,390, filed on Apr. 10, 2006, nowabandoned, and for which priority is claimed under 35 U.S.C. §120, theentire contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The invention is directed a method for positioning nanoparticles on apatterned substrate, and the use of the positioned nanoparticles to makeone-dimensional materials.

BACKGROUND OF THE INVENTION

Deposition of uniformly-thick films of insulating, semiconducting, andconducting materials is of paramount importance to the microelectronicsindustry. As the lateral feature size of circuit elements continues toshrink (in order to achieve improved circuit performance), theuniformity tolerances on film thicknesses also scales downproportionally. Conventional film deposition methods such as physicalvapor deposition, chemical vapor deposition, and atomic layer depositioncan achieve uniform thicknesses (at the precision of single atomiclayers) over extremely large areas, however such systems are costly bothto purchase and to maintain. Also, there are other lower-performancetypes of applications for microelectronics where it would be desirableto deposit uniform layers of materials without requiring highlyspecialized (and expensive) deposition systems.

Chemically-synthesized nanoparticles provide a low-cost alternativeroute to the production of materials that are highly-uniform in size andcomposition. High-temperature solution-phase synthesis is one method bywhich highly-uniform materials can be produced. Methods exist forproduction of a variety of metals, insulators, and semiconductors.Briefly stated, these methods produce solutions of inorganicnanoparticles with mean diameters tunable through the range of 1 nm to20 nm and with mean diameter standard deviations on the order of 5%.These nanoparticles are individually coated with organic surfactantsthat can be tailored to be in the range of 1-4 nm long. The surfactantprevents the nanoparticles from aggregating in solution. A schematic ofa chemically-synthesized nanoparticle is shown in FIG. 1( a).

Uniformly-sized nanoparticles can be made to organize themselves into acrystal when deposited from solution onto a substrate. Because of theiruniform size, spherically-shaped nanoparticles will pack intohexagonal-close-packed (HCP) arrangements as shown schematically in FIG.1( b). This process is often referred to as self-assembly. Nanoparticlesof other shapes will pack into different crystal arrangements. Forexample, cubic shaped nanoparticles will pack into a cubic lattice. Oneadvantage of this type of self assembly is that, because of the uniformdiameter of the nanoparticles, the resulting film has a very uniformthickness. In other words, films composed of a single layer ofnanoparticles will be uniformly one nanoparticle-diameter thick.

Additionally, there is increasing interest in utilizing nanoparticlescomposed of different materials as catalysts for growth of onedimensional (1-D) materials. This technique involves applying the(typically) metal catalysts to a surface, and then growing the1-dimensional material using a technique such as chemical vapordeposition. The size of the catalyst will heavily influence the diameterof the resulting 1-D structure. In nearly all cases of growth of thistype, the substrate (and catalyst) must be heated to high temperatures(over 400° C. and can be up to 1000° C.). However, at these hightemperatures, nanoparticle-type catalysts distributed over a surface ofa substrate will often aggregate, resulting in larger-sized catalystswith a broader size distribution (determined by metal diffusion duringaggregation), and ultimately larger-diameter 1-D materials with abroader size distribution.

In spite of the intrinsic propensity of nanoparticles to self-organizeand the potential advantages of nanoparticle films, there do not existmethods for uniformly depositing nanoparticle films over large areas,similar to conventional film deposition methods such as physical vapordeposition, sputtering, or chemical vapor deposition. Four methods fornanoparticle film deposition have been used to date:

1. Deposition from solution followed by solvent evaporation: In thismethod a solvent containing dissolved nanoparticles is deposited onto asubstrate and the solvent is removed through controlled evaporation. Asthe solvent evaporates the nanoparticles organize themselves intocrystalline layers. This method produces nicely-organized films, but thefilm thickness is uncontrolled. Layers of varying thickness forms as thesolvent evaporates.

2. Nanoparticle film deposition by substrate immersion: In this methodthe substrate is immersed into a nanoparticle-containing solution andallowed to sit. Over time, nanoparticles diffuse in solution and findtheir way to the substrate. This method produces films of uniformthicknesses, however nanoparticle layers are not close-packed and oftencontain voids (regions devoid of nanoparticles). In addition, thismethod deposits nanoparticle layers everywhere on a surface.

Langmuir-Blodgett technique: In this method a nanoparticle film isformed on a liquid surface. By compressing the film on the liquid, thenanoparticles can be made to self organize Films are transferred to asolid substrate by dip coating onto the liquid surface. This methodproduces ordered nanoparticle layers, however it is difficult to controlfilm thickness. Often films are composed either of multilayers, or elsecontain voids. Also, cracks in the film can occur due to the stress offilm transfer from liquid to solid substrate.

4. Nanoparticle film deposition by spin-casting: In this methodnanoparticle-containing solutions are spin-coated onto a solidsubstrate. After solvent evaporation, a nanoparticle film remains.Nanoparticle films produced by this method are not well-organized, dueto the non-equilibrium nature of the spin-casting process.

All of the above four methods describe depositing nanoparticle filmsover an entire surface of a substrate.

SUMMARY OF THE INVENTION

The invention is directed to a method of positioning nanoparticles on apatterned substrate. The method comprises providing a patternedsubstrate with selectively positioned recesses, and applying a solutionor suspension of nanoparticles to the patterned substrate to form awetted substrate. A wiper member is dragged across the surface of thewetted substrate to remove a portion of the applied nanoparticles fromthe wetted substrate. As a result, a substantial number of the remainingportion of the applied nanoparticles is disposed in the selectivelypositioned recesses of the substrate.

The invention is also directed to a method of making carbon nanotubes.The method comprises providing a patterned substrate with selectivelypositioned recesses, and applying a solution or suspension ofnanoparticles to the patterned substrate to form a wetted substrate. Awiper member is dragged across a surface of the wetted substrate toremove a portion of the applied nanoparticles from the wetted substrate.As a result, a substantial number of the remaining portion of theapplied nanoparticles is disposed in the selectively positionedrecesses. The positioned nanoparticles form catalytic sites on thesubstrate from which carbon nanotubes can be formed under suitableheating and reaction conditions.

The invention is also directed to an array of nanoparticles positionedin recesses of a substrate. The nanoparticles will typically have a meandiameter of from 1 nm to 50 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the present invention will become apparentupon consideration of the following detailed description of theinvention when read in conjunction with the drawings, in which:

FIG. 1( a) is a pictorial depiction of a nanoparticle with adheredsurfactant molecules;

FIG. 1( b) is a pictorial depiction of self assembled nanoparticles;

FIGS. 2( a) to 2(d) is a schematic representation of a process of theinvention;

FIG. 2( e) is a pictorial depiction of a positioning of nanoparticles ina continuous channel;

FIG. 3 is a pictorial depiction of a positioning of nanoparticles in achannel or hole with a width approximate to the diameter of thenanoparticles;

FIGS. 4( a) to 4(d) is a schematic representation of another process ofthe invention;

FIG. 5 is a pictorial depiction of a formed nanotube or nanowire;

FIG. 6 is a scanning electron micrograph (SEM) of a self assembled,porous polystyrene film on a silicon dioxide surface;

FIG. 7 is a SEM of the transferred pattern of FIG. 6 into a silicondioxide surface;

FIGS. 8( a) and 8(b) is a SEM of the transferred pattern of FIG. 7 andthe transferred pore size reduced by atomic layer deposition,respectively;

FIG. 9( a) is a SEM of the transferred pattern into a silicon substrate;

FIG. 9( b) is a SEM of the transferred pattern of FIG. 9( a) reduced bythermal oxidation;

FIG. 10 is a SEM of FIG. 7 with the positioned nanoparticles followingaction of the wiper member according to the process of the invention;and

FIGS. 11( a) and 11(b) are SEMs of carbon nanotubes formed by theprocess of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention is directed to a method of positioning nanoparticles on apatterned substrate. The method comprises: providing a substrate with apattern of recesses; applying a solution or suspension of nanoparticlesto the patterned substrate to form a wetted substrate; and dragging awiper member across a surface of the wetted substrate to remove aportion of the applied nanoparticles from the wetted substrate such thata substantial number of the remaining portion of the appliednanoparticles are disposed in the recesses.

The method can also include the additional steps of heating the wipedsubstrate with the remaining portion of the applied nanoparticlesdisposed in the selectively positioned recesses. The heating allows forthe removal of organic material, e.g., organic surfactants or polarsolvents, which can adhere to the nanoparticles. Alternatively, themethod can also include contacting the wiped substrate with a washsolution followed by dragging the wiper member across the wash-contactedsurface of the substrate. Following the wash step, the washed substratecan be heated to remove the organic material from the surface of thenanoparticle

The method provides for the deposition of nanoparticles over selectedareas of a substrate. Some of the advantages provided by the methodinclude the following.

1. The method is relatively quick. The selective positioning of thenanoparticles over several square inches of substrate can take only afew seconds.

2. The selective positioning of the nanoparticles can be conducted inair, thus expensive vacuum systems are not necessarily required.

3. The thickness of resulting films that are formed from the positionednanoparticles can be controlled by the average particle diameters of thenanoparticles. For example, a monolayer will predominately have athickness of one diameter, whereas a bilayer will predominately have athickness of two diameters.

4. The resulting action of the wiping member essentially removesnanoparticles from unwanted regions of the substrate such as a topsurface, thus providing regions of the substrate free fromnanoparticles.

5. The nanoparticle films can be aligned to other features on thesubstrate.

6. The method facilitates separation of nanoparticles on a substratesuch that the subsequent heating of the substrate, e.g., for formingone-dimensional materials such as carbon nanotubes, will not cause thenanoparticles to aggregate. As a result, the formed materials will havea uniform linear dimension or diameter.

A schematic representation of one embodiment of the invention isdepicted in FIG. 2. As shown, the initial step is to pattern a substratewith a plurality of recesses. Known lithographic techniques such asphotolithography, imprint lithography, electron- or ion-beam lithographycan be used to pattern the substrate. For example, a lithographicpattern can be transferred to a substrate using reactive-ion etching,chemical etching, ion-beam etching, or sputtering. The lithographic maskmaterial is then removed leaving the substrate 10 with a pattern ofrecesses, FIG. 2( a) (a cross-section of a single recess 12 is shown).Non-lithographic techniques such as polymer self assembly (and optionaletching step) or anodic etching of an aluminum film can also be used toprovide a patterned mask through which to form recesses in thesubstrate.

A suspension (slurry) or solution of nanoparticles 14 in a given solvent16 is applied to the patterned substrate to form a wetted substrate,FIG. 2( b). Prior to evaporation of the solvent, a wiper member 18 isplaced in contact with the wetted substrate and dragged across thesurface, FIG. 2( c). The wiper member can be made of an elastomericmaterial. For example, the wiper member can contain polydimethylsiloxane(PDMS). Of course, other elastomeric materials with properties similarto PDMS can be used as well. The wiper member is essentially used as a“squeegee” to remove nanoparticles and excess solvent from thenon-recessed areas of the substrate, and therefore, it is preferred thatthe wiper member include a uniform edge. The squeegee action also helpsto direct nanoparticles into the recessed areas of the substrate. Theaction of wetting and dragging the wiper member across the surface ofthe patterned substrate can be repeated as many times is necessary toposition the nanoparticles 14 in the recessed areas of the substrate,FIG. 2( d).

Following the positioning of the nanoparticles the substrate can bewashed or rinsed with a wash solvent. Again, the wiper member can beused to remove the excess wash solvent.

Following the positioning of the nanoparticles the substrate can beheated so as to remove organic material adhering to the surfaces of thepositioned nanoparticles. The heating can also be used to sinter thepositioned nanoparticles to form a continuous film within the recessedregions of the substrate. The top of the resulting film will be coplanarwith the substrate surface, as the nanoparticle layer is recessed belowthe substrate surface (see, FIGS. 2( d) and 2(e)). As depicted in FIGS.2( d) and 2(e), the thickness of the film can be controlled to someextent by the depth of the recess and the diameter of the nanoparticle.As a result, the process can provide greater control over thicknessuniformity of the resulting films.

In another embodiment, the depth of the patterned recesses is tallerthan a single nanoparticle diameter, such that each recess accommodatesmore than a single layer of nanoparticles, see FIG. 2( e). If thediameter of the recessed area is between one and two nanoparticlediameters wide, then multilayers of single nanoparticles stacked on topof each other can be formed, see FIG. 3. The positioned nanoparticlescan then be sintered to form continuous channels of selective materialin the substrate, e.g., formation of copper wires (from Cunanoparticles) in a dielectric substrate. The resulting copper wireswill have diameters comparable to the diameters of the originalnanoparticles.

The invention is also directed to an array of nanoparticles positionedin recesses of a substrate, wherein the nanoparticles have an averageparticle diameter of 1 nm to 50 nm. In one embodiment, the recess andthe positioned nanoparticle have a comparable diameter such that thepositioned nanoparticles are stacked within the recess. The array ofnanoparticles can then be used as a template to form one-dimensionalmaterials.

The positioning of nanoparticles on the substrate can also be used toseed the growth of one-dimensional materials such as nanowires ornanotubes. In one embodiment, the substrate 20 can be patterned suchthat individual recess volumes 22 are comparable to the particle size ofthe nanoparticles 24. If the average recess diameter is between one andtwo mean nanoparticle diameters wide, a single nanoparticle 24 will bepositioned in each recess 22, FIG. 4( d). The same method described inrelation to FIGS. 2( a) to 2(b) can be used to position thenanoparticles in each of the recess volumes as shown in FIG. 4.

Nanowires or nanotubes can be grown using known methods of chemicalvapor deposition, FIG. 5. In this instance, the nanoparticles,typically, metal or metal oxide nanoparticles, are used to seed thegrowth of the nanotube/nanowire 30. In many cases, the mean diameter ofthe resulting one-dimensional materials can be controlled by the meandiameter of the nanoparticle. One example of a one-dimensional materialthat can be made by such a template synthesis are carbon nanotubesformed by chemical vapor deposition.

The invention is also directed to a method of making carbon nanotubes.The formed carbon nanotubes can have a mean diameter of from 1 nm to 50nm, or from about 2 nm to about 10 nm. The method comprises providing asubstrate with a pattern of recesses, and applying a solution orsuspension of nanoparticles to the patterned substrate to form a wettedsubstrate. A wiper member is dragged across a surface of the wettedsubstrate to remove a portion of the applied nanoparticles from thewetted substrate such that a substantial number of the remaining portionof the applied nanoparticles are disposed in the recesses. Once thenanoparticles are positioned in the recesses, the heating of the wipedsubstrate under suitable reaction conditions provides the catalyticsites from which the carbon nanotubes form. In one embodiment, thenanoparticles comprise an iron oxide.

The carbon nanowires or carbon nanotubes are formed by any suitablegrowth technique known to those of ordinary skill. For example, thecarbon materials can be grown by chemical vapor deposition (CVD) orplasma-enhanced chemical vapor deposition (PECVD) using any suitablegaseous or vaporized carbonaceous reactant(s) including, but not limitedto, carbon monoxide, ethylene, methane, acetylene, a mixture ofacetylene and ammonia, a mixture of acetylene and dinitrogen, a mixtureof acetylene and dihydrogen, and xylene under growth conditions suitablefor promoting carbon growth on the positioned nanoparticles. In suchdeposition processes, the substrate is typically heated to a temperatureadequate to promote and/or hasten CVD growth. Additives may be mixedwith the reactant to encourage the synthesis of single-wall nanotubes,the synthesis of multi-wall nanotubes, or to increase the nanotubelengthening rate or length.

The reactant chemically reacts with the nanoparticle to nucleate thecarbon materials and to sustain their growth following nucleation. Onesuch carbon material that can be grown are carbon nanotubes. Carbonnanotubes are typically described as hollow cylindrical tubes composedof precisely arranged hexagonal rings of bonded carbon atoms. The carbonnanotubes may be multi-wall nanotubes resembling concentric cylinders ormay be single-wall nanotubes. The carbon nanotubes will generally extendfrom the positioned nanoparticle(s) in a direction generallyperpendicular to or in an approximately perpendicular orientation to thehorizontal surface of the substrate. The carbon nanotubes are expectedto have a statistical distribution of heights or lengths.

In one embodiment, single-wall nanotubes can be grown from thepositioned nanoparticle(s) as described in U.S. patent application Ser.No. 10/689,675, filed Oct. 22, 2003 and assigned to InternationalBusiness Machines Corporation, the entire disclosure of which isincorporated herein by reference. This patent application describes howone of ordinary skill can control the diameter of CVD or PECVD growncarbon nanotubes based on the control of the residence time of the gasesin the reactor such as by controlling the pressure, or the gas flowrates, or a combination of both. As defined by Grill in “Cold Plasma inMaterials Fabrication From Fundamentals to Applications” published byIEEE press, 1994, page 91, the gas residence time is: t_(r)=_(P)vol_(r)/Q; wherein p=pressure (atmospheres), vol_(r)=volume of reactor(cm³) and Q=total mass flow (sccm). The gas residence time is a measureof the average time of the gas in the reactor. Thus, if the flow isconstant and the pressure increases, the residence time increases, andif the pressure is constant and the flow increases the residence timedecreases. The residence time is typically about 1 minute to about 20minutes and more typically about 1 to about 10 minutes. The residencetime is typically determined by controlling the pressure, flow or boththe pressure and flow in the reactor. By varying the residence time (e.ggrowth pressure and/or flow rates) of the precursor gases in the CVD orPECVD reactor, carbon nanotubes with diameters from about 0.2 nanometersto several nanometers can be formed.

In the process of the invention, any known substrate material can beused including silicon, silicon dioxide, silicon nitride, and metalssuch as aluminum, tungsten, copper, gold, or platinum.

In one embodiment, a porous polymer film was formed on a thin layer (40nm) of silicon dioxide that had been grown by thermal oxidation on asilicon substrate. The porous polymer film was then patterned using adiblock copolymer patterning technique similar to that described in theliterature (see, for example, K. W. Guarini et al., Advanced Materials,14 1290 (2002), or T. Thurn-Albrecht et al., Advanced Materials, 12, 787(2000), or references contained therein). For instance, a randomcopolymer brush layer was formed on the silicon dioxide film (substrate)by spin-casting from a dilute solution, followed by thermal annealing,and a subsequent solvent rinse. A diblock copolymer film comprisingpolystyrene (PS) and polymethylmethacrylate (PMMA) of appropriatethickness was applied to this surface by spin-casting, and it wasallowed to self assemble by thermal annealing. After annealing, thepolymer-coated substrate was exposed to ultraviolet light (this step isoptional) and immersed in acetic acid, followed by a water rinse anddried in nitrogen. The resulting film comprised a porous polystyrenematerial with pores hexagonally arranged on the surface. The pore sizeand spacing depend on the molecular weight of the diblock copolymer. Inthis embodiment, for example, the pore size was about 20 nm in diameterwith about a 40 nm pore center to center distance. FIG. 6 is a scanningelectron microscope (SEM) image of the resulting porous PS film.

The porous PS pattern was then transferred to the underlying silicondioxide film using plasma etching. Other possible techniques one can useinclude wet chemical etching, ion beam etching, or physical sputtering.After plasma etching, the PS film was removed using an oxygen plasma.One can also use organic solvent, acids, or ozone to remove the PS. AnSEM image of the resulting porous oxide film is shown in FIG. 7. Thedepth of the pores can be controlled by the plasma etch time, while thepore diameter and spacing are dictated by the formed PS film dependingon the application of the patterned substrate. In this embodiment, forexample, the oxide pore diameters were about 20 nm with spacings ofabout 40 nm, and pore depths were from 10 nm to 40 nm.

The resulting pore size can be further adjusted by one or more chemicaltechniques. For example, one can use a conformal film deposition (suchas atomic layer deposition, chemical vapor deposition, or sputtering)onto the porous oxide surface. For instance, we were able to decreasethe pore diameters with atomic layer deposition of tantalum nitride ontothe oxide surface as shown in FIGS. 8( a) and 8(b). In this case, thepore diameter was reduced by about 45% to about 14 nm (starting fromabout 26 nm). The chemical techniques that are used to shrink pore meanpore diameters can reduce the mean pore diameter to about 10 nm, or assmall as about 5 nm. Note that this technique does not change the porespacing, but only the pore diameter.

Alternatively, if the substrate had been silicon rather than silicondioxide, one could use thermal oxidation as a method for shrinking poresize. Oxidation of a porous silicon surface reduces the pore dimensionsbecause oxide occupies roughly twice the volume of silicon. The resultsof such a process is shown in FIGS. 9( a) and 9(b).

A solution of nanoparticles with a mean diameter of 14 nm in octanesolvent was applied to the porous substrate shown in FIG. 7. Theconcentration of the nanoparticles in the solvent was less than 1% byweight. The substrate surface is then wetted with the suspension(nanoparticle containing solution) by completely covering the substratewith the suspension. This is accomplished by depositing the suspensionwith a pipette, or alternatively the substrate can be immersed in thenanoparticle suspension.

The nanoparticles used in the process of the invention are generallymonodisperse in diameter and, on many occasions, have a mean diameternot too different from the mean pore diameter of the porous surface.Typical mean nanoparticle diameter is from about 1 nm to 20 nm with astandard deviation of less than about 15% of the mean diameter.Optimally, the mean nanoparticle diameter distributions are less than 5%of the mean diameter. The nanoparticles can be dispersed in an organicsolvent such as hexane, octane, decane, or dodecane, or mixturesthereof.

While the substrate was still wet with the nanoparticle containingsolution, an elastomeric wiper (squeegee) was placed in contact with thesubstrate and wiped across the surface. The wiping action of thesqueegee removed excess nanoparticle containing liquid from thesubstrate. It may be advantageous to pre-wet the wiper with a cleansolvent (hexane, octane, etc). Also, the wiper can be moved across thesurface any number of times.

If the mean nanoparticle diameter is roughly matched in size with thepores of the substrate surface, then single nanoparticles will bedeposited in a majority of the pores on the surface. FIG. 10 shows ascanning electron microscope image of one such porous surface, whereover 90% of the pores have been filled with a single nanoparticle. Inthis case, the nanoparticles are comprised of iron oxide, and have meandiameters of 14 nm.

Following placement of the single nanoparticles in a majority of thepores of the substrate, the nanoparticles were used as catalytic sitesfor carbon nanotube growth. One advantage of this technique is that thenanoparticles are physically confined to the substrate pores and arethus prevented from aggregating during the high temperature nanotubegrowth process. For example, placement of the pore filled substrate in atube furnace resulted in the formation of carbon nanotubes usingchemical vapor deposition. The tube furnace was heated to a temperatureof 800° C. while flowing hydrocarbon-containing gas. FIGS. 11( a) and11(b) show the resulting multiwall carbon nanotubes grown fromindividual catalysts placed on the substrate.

We claim:
 1. One-dimensional materials prepared from an array ofnanoparticles positioned in one or more recesses of a substrate, whereinthe recesses and the positioned nanoparticles have a comparable diameterof the same order of magnitude such that one nanoparticle is positionedwithin each of the one or more recesses; wherein a depth of the one ormore recesses is from 10 nm to 40 nm; and wherein a diameter of the oneor more recesses is adjusted by conformal film deposition and is betweenone and two times the mean diameter of the nanoparticles, and whereinthe nanoparticles have a mean diameter of from 1 nm to 50 nm, andwherein the nanoparticles are catalytic sites for the growth of theone-dimensional materials.
 2. The one dimensional materials of claim 1,being carbon nanotubes formed by chemical vapor deposition.
 3. The onedimensional materials of claim 1, the one dimensional materials beingsingle-wall carbon nanotubes formed by chemical vapor deposition.
 4. Theone dimensional materials of claim 3, wherein the single-wall carbonnanotubes have a mean diameter of from 1 nm to 50 nm.
 5. The onedimensional materials of claim 3, wherein the single-wall carbonnanotubes have a mean diameter of from 2 nm to about 10 nm.
 6. The onedimensional materials of claim 1, wherein the nanoparticle comprise aniron oxide.
 7. The one dimensional materials of claim 1, wherein adiameter of the one or more recesses is reduced by thermal oxidation. 8.The one dimensional materials of claim 1, wherein the nanoparticles havea mean diameter of from 1 nm to 20 nm.
 9. The one dimensional materialsof claim 8, wherein the nanoparticles have a standard deviation of lessthan about 15% of the mean diameter.
 10. The one dimensional materialsof claim 8, wherein the nanoparticles have a standard deviation of lessthan about 5% of the mean diameter.